The present invention relates to the preparation and use of the xe2x80x9ccalcium analoguexe2x80x9d alkaline-earth radionuclide radium-223 for the targeting of calcified tissues, e.g., bone and a physiological acceptable solution comprising 223Ra.
Biomedical use of radionuclides for pain palliation and/or cancer treatment, including prophylactic treatment of bone surfaces to slow down/inactivate undetectable metastases has previously been based upon xcex2-emitters and conversion electron emitters.
A substantial percentage of cancer patients is affected by skeletal metastases. As many as 85% of patients with advanced lung, prostate and breast carcinoma develop bony metastases (Garret, 1993; Nielsen et al., 1991). Established treatments such as hormone therapy, chemotherapy and external radiotherapy often causes temporary responses, but ultimately most bone cancer patients experience relapses (Kanis, 1995). There is thus a strong need for new therapies to relieve pain and slow down tumor progression. Bone targeting radioisotopes has been included in clinical trials for the treatment of cancer to the skeleton (De Klerk et al., 1992, Foss{dot over (a)} et al., 1992, Lee et al., 1996, Silberstein, 1996). These radiopharmaceuticals have been based on xcex2-particle emitters (Atkins, 1998) and lately also a conversion electron ermitter (Atkins et al., 1995).Among these compounds which have so far been approved by US Food and Drug Administration, Le. are strontium-89 (Metastron(trademark)) and 153Sm EDTMP (Lexidronam(trademark)). The strontium-89 compound can only be administered in amounts sufficient for pain palliation, not for tumor therapy, because a significant myelotoxicity occurs before significant antitumour therapeutic dose levels can be reached (Silberman, 1996).
Recently, one of the inventors authored a publication (Larsen et al., 1999) showing by dosimetry that xcex1-emitters can be more advantageous than xcex2-emitters as bone seekers. I.e. the shorter range of the xcex1-emitters effecting less bone marrow exposure when the source is located at bone surfaces. In this study two xcex2-emitting bisphosphonate bone seekers were compared with two xcex2-emitting compounds with similar chemical structures and bone affinity. Dosimetric calculations indicated that, in mice, the bone surface to bone marrow dose ratios were approximately 3 times higher with the xcex1-emitter compared to the xcex2-emitter. This indicates that xcex2-emitting bone seekers may have advantages over xcex2- and/or electron emitting compounds because the radiation dose can be more strongly concentrated to the bone surfaces. Because of the short half life (txc2xd=7.2 h) and since its production is limited to only a few sites worldwide, astatine-211 is at present not yet available for large scale marketing. Besides astatine-211 only a few xcex1-particle emitting radioisotopes are at present considered useful for biomedical applications (Feinendegen et al., 1997). The lead-212/bismuth-212 system has previously been used for preparation of bone seeking agents. Bismuth-212 complexed with ethylene-diamine-tetra(methylene-phosphonic acid) (EDTMP), or 1,4,7,10-tetraazacyclododecane 1,4,7,10-tetra(methylene-phosphonic acid) (DOTMP), showed a significant bone affinity. But because of the short half life of bismuth-212 (txc2xd=60.6 min), normal tissue exposure during the uptake phase of the radiopharmaceutical would be considerable (Hassfjell et al., 1994, 1997). This would be ever more pronounced with the other xcex1-emitting bismuth isotope considered for biomedical use, the bismuth-213 (txc2xd=46 min). Attempts have been made to use the xcex2-emitter lead-212 (txc2xd=10.6 h) as an in vivo generator for 212Bi. However, a significant translocation affecting a high kidney accumulation of the xcex1-emitter was observed (Hassfjell et al., 1997). Other xcex1-emitting radioisotopes potentially useful for biomedical applications are the radium isotopes 224 and 226. As with other group II alkaline-earth metals, radium in its cationic state is a natural boneseeker.
Previously the radium isotopes 224 and 226 has been studied, partly because of their bone affinity (Loyd et al., 1982, 1991; Muggenburg et al., 1996, Mxc3xcller, 1971; Raabe et al., 1993; Rundo, 1978). Radium-226 is, because of its long half-life (1600 years) and its noble gas radon-222 daughter (txc2xd=3.8 days), not considered useful for targeted radionuclide therapy. Because of its chemical nature, radon is inert to chemical bonding under in vivo conditions. It can therefore readily translocate in vivo when generated from the decay of the mother nuclide (Rundo, 1978). Inhaled radon mainly dissolves in body fluid and fat and is mainly eliminated from the body by exhalation (Rundo, 1978). In an experiment using bone samples, Lloyd and Bruenger (1991) reported that 89.5-94.25% of the radon-222 escaped from the bone after radium-226 had been administered to dogs. In contrast to radium-226, radium-224 has a half life (txc2xd=3.64 days) which seems very suitable for biomedical applications. 224Ra was used medically for many years to treat ankylosing spondylitis (Delikan, 1978). Unfortunately, also a significant fraction of the daughter isotopes of radium-224 escaped from bone, probably mainly because of the radon-220 (txc2xd of 55.6 s) daughter (Lloyd et al., 1982; Mxc3xcller et al., 1971; Rundo, 1978).
It is thus known from previous studies that when the radium isotopes 224Ra and 226Ra were incorporated in bone, a significant translocalisation of their radon daughters occurred, which could, at least partly, explain the known carcinogenic effect of these two radium isotopes. This may be one of the reasons why (xcex1-emitters have not been evaluated clinically as bone seeking radiopharmaceutical against skeletal cancers.
It is the object of the present invention to provide a bone seeking radionuclide useful as a pharmaceutical agent, showing that radioactive decay products from its transformation do not translocalize significantly after its incorporation in bone (valid at least after 3 days from administration).
The present inventors made the significant and somewhat unexpected discovery that from 223Ra localized in bone, very little translocation of the radon daughter (as well as other radionuclides from the decay chain) occurred. Hence, the 223Ra series may be used to irradiate the bone surface without any significant translocation of radionuclides (including diffusion into bone marrow). Furthermore radium-223, should be more suitable as a boneseeking radiopharmaceutical since the half life (11.4 days) is about three times that of 224Ra, allowing a deeper incorporation into the matrix of the bone surfaces before decay occurs. Also, perhaps even more important, the radon daughter radon-219 has a short half-life (3.9 seconds), which should diminish translocation in, or as a result from the radon step. Three of the four xcex2-particles emitted during decay of 223Ra and daughter nuclides are emitted immediately following 223Ra transformation (Seelman-Eggebert et al., 1981), i.e., of the first three transformations following 223Ra, the 3.9 second 219Rn alpha decay is the one with the longest half life (Table 1). The last xcex1-emitter in the 223Ra chain, 211Bi (txc2xd=2.15 min) follows the decay of the xcex2-emitter lead-211 (txc2xd=36.1 min) and may therefore show some translocation. However, if the precursor, lead-211, is trapped inside of the bone matrix, also the last xcex1-particle in the 223Ra series may be delivered to the bone surface area. In addition xcex1-particles are high linear energy transfer (high-LET) radiation that is extremely cytotoxic to mammalian cells (Hall, 1994; Ritter et al., 1977). An xcex1-particle emitting radiation source localized in target tissue can deliver radiation to a smaller target area, thus reducing normal tissue exposure compared to xcex2-emitters.
The present invention relates to the preparation and the use of the xe2x80x9ccalcium analoguexe2x80x9d alkaline-earth radionuclide radium-223 for the targeting of calcified tissues, e.g., bone and a physiological acceptable solution comprising 223Ra.
In this patent application the inventors have invented a novel use of 223Ra, i.e., as an xcex1-emitting radiopharmaceutical for targeting of calcified tissues, e.g., bone surfaces and osseous tumor lesions. As indicated by the properties of the radionuclide(s) as well as the experimental examples presented in the present patent application, radium-223 can be suitable as a bone seeking radio-pharmaceutical. As an example, the invention may be used for prophylactic cancer treatment by delivering a focused dose to bone surfaces in patients with a high probability of having undetected micrometastases at bone surfaces. Another example of its potential use would be in the treatment of painful osseous sites in a similar fashion as the previously described xcex2- and electron emitting radiopharmaceuticals for bone pain palliation.
Radium-223 localized onto the bone surfaces and/or in calcified tumors can, together with its daughter nuclides, deliver an intense and highly local dose of xcex1-particles with less bone marrow dose compared to currently used xcex2-emitting and/or electron emitting radiopharmaceuticals. Skeletal diseases, e.g., primary or metastatic cancer to the bone may be treated with the 223Ra radiopharmaceutical.
The present invention includes the use of the nuclide as a cationic species and/or associated to a chelator or another form of a carrier molecule with affinity for calcified tissues. This also includes, but are not limited to the combination of radium-223 with a chelator that can be subsequently conjugated to a molecule with affinity for calcified tissues. The intent is to use the radioisotope to generate a cascade of xcex1-particles on bone surfaces and/or in calcified tumors for the palliation of pain caused by various diseases and/or for the prophylactic use against possible minimal disease to the skeleton, and/or also for the therapeutic treatment of established cancer to the bone. The diseases where the radioisotopes could be used includes, but are not limited to skeletal metastases of prostate-, breast-, kidney- and lung cancer as well as primary bone cancer and also multiple myeloma.
Radium-223 solutions are prepared for use in the targeting of calcified tissues or for bone surface irradiation. The following examples are showing a high and selective uptake of the 223Ra in bone with very little relocalization of daughter nuclides. This shows that bone surfaces can be sterilized to inactivate microscopical deposits of cancer cells and also that calcified cancerous lesions can be irradiated either for palliation or therapy with this isotope. The compound differs from other commonly used radiopharmaceuticals with bone affinity because the main dose component comes from xcex1-particles which has a much shorter range compared to the frequently used beta and electron emitters. Therefore the dose delivered to red bone marrow can be significantly reduced with this new compound, i.e., myelotoxicity is likely to be reduced. Radium-223 differs from the previously used medical radionuclide radium-224 in the following: (1) 223Ra has a significantly longer half-life affecting better bone to soft tissue ratios because a significantly larger fraction of this isotope would be eliminated from the soft tissues before decay occurs. (2) Longer half life also allows a deeper incorporation of the radionuclide into the bone surfaces as the bone synthesis progresses, potentially improving retention of daughter isotopes which may otherwise translocate because of chemical diffusion and nuclear recoil. (3) Also the shorter half life of the 219Rn from 223Ra compared to the 220Rn from 224Ra, ensures less translocation of daughter nuclides from the 223Ra series.
The 223Ra salt or derivative thereof will be administered to a mammal, such as a human, in need thereof by all available administration routes, such as oral, subcutaneous, intravenous, intraarterial or transcutane. Preferably the active compound is administered by injection or infusion.
Oral administration is performed by use of tablets, capsules, powders or in liquid form, such as suspension, solution, syrup or emulsion. When formed into tablets conventional expicients, lubricating agents and binding agents are used. When administered as liquids conventional liquid carriers are used. When administered as injection or infusion solutions the carrier is preferably isotonic saline, with or without agent(s) to stabilize the radium cation to prevent precipitation of radium salts or insoluble complexes.
The active principle according to the invention could be used both in prophylactic, palliative and therapeutic treatment of non-malignant and malignant diseases affecting bones and soft tissues. The malignant diseases are selected from the group consisting of prostate cancer, breast cancer, kidney and urinary cancer, primary bone cancer, lung cancer and multiple myeloma, and the non-malignant disease are selected from the group consisting of autoimmune diseases affecting joints and skeleton, e.g. rheumatoid arthritis, schleroderma and spondyloartropathies.
The physiologically acceptable preparation for in vivo administration according to the present invention comprises dissolved radium-223 salt, with or without a single or a combination of several cations, as stabilizing alkaline earth metal cation analogue carrier, with or without an agent to prevent precipitation and/or generation of colloids, in addition to pharmacologically acceptable carriers and adjuvans. The cation acting as stabilizing alkaline earth metal cation can be selected from the group consisting of magnesium, calcium and strontium. Furthermore, the agent to prevent precipitation and/or generation of colloids is a carboxylic acid or a combination of carboxylic acids, such as oxalic acid, oxaloacetic acid, tartaric acid, succinic acid, malic acid and malonic acid. The concentrations of the compounds in the preparation will generally be less than the individual LD 50 dose, for example less than 20% of the LD 50 dose, and thus vary for the different components. The activity of 223Ra will be dependent upon the type and route of administration and the underlying condition or disease and-will vary between approximately 50 kBq to approximately 10 MBq, administered in single or multiple doses for mammals, such as for example humans.
According to the invention radium-223 is furthermore used to produce a pharmaceutically active preparation to treat non-malignant and malignant diseases affecting bone, bone surfaces and soft tissues, both palliative and therapeutically.
The preparation is administered to the mammal, such as humans or animals ,i.e. dogs, in need thereof, in a palliative or therapeutically effective amount.
According to the invention radium-223 can be used in a combination therapy, wherein the 223Ra preparation is combined with the following classes of treatment; chemotherapy including bisphosphonates, surgery, external beam irradiation, low-LET radiation emitting bone seeking radiopharmaceuticals, and hormonal treatment.
The invention is furthermore directed to a kit including 223Ra produced according to the inventive method, cations as stabilizing alkaline earth metal cation analogue carrier according and an agent to prevent precipitation and/or generation of colloids in addition to pharmaceutically acceptable carriers and suitable administration equipment.
In the following the present invention is described in detail by examples which in no way is intended to limit the scope of the invention as described by the enclosed claims.
Table 1 presents the physical properties of radium-223 and its daughter nuclides (Ekstrxc3x6m et al., 1989). The decay of the 223Ra and its daughters causes the emissions of four xcex1-particles. Such a cascade of xcex1-particles can deliver a large radiation dose to a limited volume. Radium-223 therefore possesses extreme cytotoxicity, also compared to most xcex1-emitters (Howell et al, 1997).
The following shows the Radium-223 and its daughters decay series (half life and mode of decay in brackets):
223Ra (11.4 d., xcex1)  219Rn (3.9 s., xcex1)  215Po (1.8 ms., xcex1)  211Pb
(36,1 min., xcex2xe2x88x92)  211Bi (2.15 min., xcex1)  207Tl (4,8 min., xcex2xe2x88x92)  207Pb(stable)
The combined energy from the emitted radiation associated with the complete decay of 223Ra and daughters: xcx9c27.5 MeV
Fraction of energy emitted as (xcex1-particles: xe2x89xa796%
Fraction of energy emitted as xcex2-particles: xe2x89xa63%
Some gamma radiation ( less than 0,3 MeV total) is also emitted during decay and can be used to determine the quality and quantity of isotopes in samples using gamma spectroscopy. E.g. radium-223 has a characteristic gamma peak at 154.19 keV (5.59% abundance), radon-219 has a peak at 401.78 keV (6,6%) and bismuth-211 has a 351.0 keV peak (12.8%) (Ekstrom et al., 1989). These can be used to determine if redistribution occurs for daughter isotopes in vivo. Also 223Ra has a 269.41 keV peak with 13.6% abundance, but this may be difficult to distinguish from a 271.23 keV peak, with 9.9% abundance of 219Rn.
Production methods has been described for Radium-223 (Atcher et al., 1989; Howell et al., 1997). 223Ra is a member of a natural radioactive family originating from U (txc2xd=7xc3x97108 y.) via 231Th (txc2xd=25.6 y.) and the sequence 231Thxe2x86x92231Pa (txc2xd=3.3xc3x97104 y.)xe2x86x92227Ac (txc2xd=21.7 y.)xe2x86x92227Th (txc2xd=18.7 d.)xe2x86x92223Ra (11.4 d.). Atcher et al. (1989) used a cation exchange system (Bio-rad AG 50) to produce 223Ra from 227Ac. Howell et al. (1997) used the 226Ra (n,xcex3)227Ra nuclear reaction to produce 223Ra. 227Ra (txc2xd=42 min) is rapidly transformed into 227Ac (txc2xd=21.77 years) which may be separated by different methods from the 226Ra target material. Howell et al (1997) separated the 227Ac chemically from a target solution. After that was 227Ac, together with its daughter products, transferred to an anion exchange column that retained 227Th, while the mother and daughter of this nuclide was eluted. Ten days later 223Ra could be eluted from the ion exchange column. If clinical batches were to be prepared by use of the generator principle, the application of ion exchange columns based on an organic backbone may be suboptimal because radiolysis may prevent long term multiple use of a radium generator based on this type of materials (Atcher et al., 1989).
Recently new materials have been developed, and are now commercial available, that are useful for separation of actinide radionuclides (selectivity for f-elements versus alkaline earth elements). These are based on silica particles covalently bound to or impregnated with active groups. Columns can be prepared using this material allowing the elution of some elements at conditions that can retain other elements. It would also be possible to use the active groups for the separation in wet/wet extraction systems using an organic and an aqueous phase.